Composite Structural Member And Method For Producing The Same

ABSTRACT

A composite structural member is provided. The structural member includes a tubular shaft having a mating region of stiffness, and possibly thickness, greater than another region of said shaft. The shaft defines a lumen, and a fitting is disposed in the lumen. The fitting has a coupling region that defines at least one recessed portion bounded by one or more non-recessed portions, and the mating region mates with the coupling region of said fitting. As such, the shaft and fitting are mechanically restrained from at least some relative movement due to interference of the shaft and the fitting. A sleeve may be coupled to said shaft, for example, by including a tubular inner surface that proximately surrounds at least part of said shaft and mating region, for discouraging expansion of the mating region of said shaft.

FIELD OF THE INVENTION

Embodiments of the invention are directed to composite structuralmembers and methods for making the same, and more particularly tocomposite structural members including parts that interfere with oneanother.

BACKGROUND OF THE INVENTION

Traditionally, commercial airplanes were constructed with structuralcomponents composed mainly of aluminum. Such structural componentsexhibited significant strength and resistance to degradation at elevatedtemperatures, and were therefore desirable. In more recent times,commercial airplanes in increasing numbers are being designed andconstructed so as to incorporate composite structural components,meaning these components incorporate elements of metal and elementscomposed of other materials. One of the most common classes ofnon-metallic material to be used in aircraft construction ispolymer-based materials. These materials are relatively lightweight andeasily (and, therefore, inexpensively) formed into complex geometries,and as such, designers are using those materials in increasing amounts.This becomes increasingly evident as new reinforcement methods forresin-based, including new reinforcement schemes in fiber-reinforcedresin materials, are developed, thereby increasing the strength of theoverall composite material. Still, some components are required towithstand large forces or temperatures, and for these, aluminum oranother metal is usually preferred.

More recently, the aerospace industry has begun to utilize componentsthat contain both metallic and resin-based elements assembled into oneintegrated part. This practice utilizes the advantageous features ofboth classes of materials by combining targeted use of metal elements instrength-critical areas with supplemental use of structurally efficientresin-based materials in other areas. However, the integration ofmetallic and resin parts involves several challenges. One of the mostprominent is maintaining the integrity of the bond between the metal andresin parts. In many cases, such composite parts are bonded using anadhesive, such as epoxy. Residual stresses present in joints between themetal and resin parts, due to the large mismatch of thermal expansioncoefficients that often exists between metals and resins, can be greatenough to cause de-bonding of the metal and resin elements. Further, theareas where different parts are fastened together often include stressconcentrations that can lead to failure. Finally, the adhesive strengthbetween the epoxy and the adjacent parts, as well as the cohesivestrength of the epoxy itself, can be reduced when compared to thestrength of the component parts. For all of these reasons, failure ofcomposite structural members due to failure of the joints between themetal and resin-based components is a significant issue, and there is aneed in the art for an improved method for creating composite structuralcomponents in which the integrity of the coupling between the elementsof the composite structural component is enhanced.

SUMMARY OF THE INVENTION

Embodiments of the present invention may address at least some of theabove issues while potentially providing still other advantages byproviding composite structural members and methods for making the same.The composite structural members include parts that interfere with oneanother, thereby discouraging at least some relative movements betweenthe parts.

One aspect of the present invention is directed to a compositestructural member. The structural member includes a tubular shaft havinga mating region of stiffness, and possibly thickness, greater thananother region of said shaft. The shaft defines a lumen, and a fittingis disposed in the lumen. The fitting has a coupling region that definesat least one recessed portion bounded by one or more non-recessedportions, and the mating region mates with the coupling region of saidfitting. As such, the shaft and fitting are mechanically restrained fromat least some relative movement due to interference of the shaft and thefitting. Adhesive may be disposed between the coupling region of saidfitting and the mating region of said shaft. A sleeve may be coupled tosaid shaft, for example, by positioning a tubular inner surface of thesleeve so as to proximately surround at least part of said shaft andmating region, for discouraging expansion of the mating region of saidshaft. The shaft and fitting and the tubular inner surface of saidsleeve may be tapered, and/or adhesive may be disposed between the shaftand sleeve. The fitting can include a shoulder that contacts the sleevewhile the inner surface of the sleeve remains substantially parallelwith an outer surface of the shaft.

In one embodiment, the recessed portion extends circumferentially aroundthe fitting to form a neck. In another embodiment, the structural memberfurther includes a core disposed in at least part of the lumen of theshaft. In yet another embodiment, the shaft is composed at leastpartially of fiber reinforced material and the mating region includes anincreased amount of fibers oriented substantially circumferentiallyrelative to another region of the shaft.

Another aspect of the present invention is directed to another compositestructural member. The structural member includes a fitting having acoupling region. The coupling region defines at least one of aprotrusion or a recessed portion bounded by one or more non-recessedportions. A tubular shaft is also included, the shaft having a matingregion and defining a lumen. The shaft is composed at least partially ofmaterial including reinforcing fibers, and is configured to have moresubstantially circumferential fibers in the mating region than inanother region of the shaft. The fitting is disposed in the lumen of theshaft such that the mating region of the shaft mates with the couplingregion of the fitting and the shaft and fitting are mechanicallyrestrained from at least some relative movement due to interference ofthe shaft and the fitting.

Yet another aspect of the present invention is directed to a method forproducing a composite structural member. The method includes providing afitting that has a coupling region with an outer surface defining atleast one recessed portion bounded by one or more non-recessed portions.A shaft is formed around the fitting, for example, by resin transfermolding or laying up of one or more sheets, such that a mating region ofthe shaft is radially adjacent to the coupling region and mating withthe recessed portion of the outer surface. Material is then added to themating region, in some embodiments such that fibers in the material arepreferentially oriented substantially circumferentially with respect toan axis defined by the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a perspective view of a composite structural memberconstructed in accordance with an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1, showingthe internal structure of the composite structural member of FIG. 1;

FIG. 3 a is a perspective view in partial cross-section of the shaft andfitting of the composite structural member of FIG. 1;

FIG. 3 b is an exploded perspective view, in partial cross-section, ofthe composite structural member of FIG. 1;

FIG. 4 is an exploded perspective view of the composite structuralmember of FIG. 1;

FIGS. 5 a-d are perspective views, at various sequential stages ofassembly according to an embodiment of the present invention, of thecomposite structural member of FIG. 1;

FIG. 6 is a perspective view of a fitting for a composite structuralmember constructed in accordance with another embodiment of the presentinvention, the fitting including a depression;

FIG. 7 is a perspective view of a composite structural memberincorporating the fitting of FIG. 6; and

FIG. 8 is a cross-sectional view of a composite structural memberconstructed in accordance with yet another embodiment of the presentinvention, in which a core is disposed in the lumen of the shaft.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring to FIG. 1, therein is shown a composite structural member 100constructed in accordance with an embodiment of the present invention.The composite structural member 100 includes a tubular shaft 110 coupledto an end fittings 120. The end fittings are configured to accept a pin,although many other types of end fittings would also be compatible withother embodiments of the present invention. The composite structuralmember may also include sleeves 140 that are substantially concentricwith and surround parts of shaft 110 and end fittings 120, as describedfurther below. Although the shaft, end fittings, and sleeves are allshown to be cylindrical, these components could have other crosssectional shapes.

Referring to FIGS. 2-4, fitting 120 includes a coupling region 122 thatextends into a lumen 112 defined by shaft 110. Coupling region 122defines a recessed portion in the form of a neck 124, and shaft 110includes a mating region 114 with an internal profile similar to that ofneck 124. As mentioned, the neck 124 may be circular in cross section,this shape possibly facilitating the manufacturing process, or the neck124 may be some other shape, such as a polygonal shape, that aids indiscouraging relative rotation of the assembled shaft 110 and fitting120. Mating region 114 is in close radial proximity to coupling region122 such that mating region 114 mates with coupling region 122, thismating serving to mechanically restrain relative movement of shaft 110and fitting 120. Specifically, mechanical interference between shaft 110and fitting 120 discourage relative movement along an axis a defined byshaft 110. In some embodiments, adhesive is disposed between shaft 110and fitting 120. This adherence serves to further discourage relativemovement along the axis defined by the shaft 110, and also to discourageor prevent relative rotation of shaft 110 and fitting 120.

Mating region 114 generally has a stiffness, and often a strength,greater than a non-mating portion 115 of the shaft, for example, due toan increased thickness of shaft 110 in the mating region 114 as comparedto the non-mating region 115. Stiffness of the mating region 114 can beincreased in ways other than or in addition to increased thickness. Forexample, a stiffer material can be used to form the mating region asopposed to that used to form the non-mating region. As another example,the material forming the mating region could be preferentiallyreinforced when compared to the material forming the non-mating portion.For example, if the material forming the shaft is fiber-reinforcedresin, more fibers could be included and/or oriented to increase thestiffness of the mating region as compared to the non-mating region. Insome embodiments, the shaft can be constructed to have anisotropicstiffness, such that the stiffness of the mating region is increased forradial expansions of the shaft, but not for axial elongation of theshaft. For example, shaft 110 can be comprised of fiber reinforcedmaterial and the mating region 114 can include an increased amount offibers oriented substantially circumferentially relative to non-matingregion 115.

In this way, the increased stiffness of mating region 114 inhibitsradial expansion of the mating region 114 of shaft 110 upon loading ofthe composite structural member 100. Such a radial expansion could leadto separation of shaft 110 and fitting 120. The sleeve 140 has a tubularinner surface 141 that proximately surrounds at least part of matingregion 114, and in some embodiments, part of the non-mating region 115as well, further discouraging separation of shaft 110 and fitting 120.In one embodiment, sleeve 140 is compressed around shaft 110, therebyincreasing the amount of contact between sleeve 140 and shaft 110 aswell as enhancing the mechanical coupling of those two components. Inanother embodiment, adhesive is disposed between shaft 110 and sleeve140 in order to secure sleeve 140. In yet another embodiment, thecoupling between shaft 110 and fitting 120 may be sufficiently strongrelative to the loading conditions of the member 100 to obviate the needfor a sleeve.

Referring to FIGS. 5 a-d, therein is shown one method for producing thecomposite structural member 100 (FIG. 1). A fitting 120 is provided, thefitting having a coupling region 122 with an outer surface 123 thatdefines a neck 124 in the manner discussed previously. The fitting istypically metallic, such as of aluminum, but may be formed of othermaterials including combinations of materials. A mandrel 150 is extendedthrough an opening in fitting 120, and one or more sheets 116 of uncuredpolymer-based material or dry fibers for resin injection are laid uparound fitting 120 and mandrel 150 to form shaft 110. Sheet 116 isconfigured such that it overlaps with neck 124 as it is being laid uparound fitting 120. During lay up, fitting 120 and mandrel 150 providesupport for sheet 116, which is typically quite flexible due to thesmall thickness of the sheet and the fact that the sheet 116 is uncured.Consequentially, shaft 110 formed of sheet 116 generally assumes a shapedefined by the outer surfaces of fitting 120 and mandrel 150.Specifically, shaft 110 includes a mating region 114 that closelyfollows the contour of neck 124. Once sheet 116 is laid up to form shaft110, sheet 116 is cured to increase rigidity of the shaft 110 and tocause shaft 110 to adhere to fitting 120. After cure, a mating region114 of shaft 110 is radially adjacent to the coupling region 122 of thefitting 120 and mating with the neck 124. After cure, the mandrel 150may be removed from the composite structural member.

Once shaft 110 has been formed around fitting 120, additional matingregion material 130 may be placed onto the mating region 114 of shaft110. Additional mating region material 130 is applied to mating region114 so that the material 130 sits in the recess defined by neck.Material 130 may be applied partially or completely around shaft 110.Once material 130 is applied, the assembly is cured to increase rigidityof the additional material 130 and, therefore, the shaft 110, as well asto cause material 130 to adhere to shaft 110. As such, radial expansionor deformation of shaft 110 is largely prevented, as is anyconsequential axial separation of shaft 110 and fitting 120. In someembodiments, the portion of the shaft 110 disposed within the recess,including the additional material 130, serves to effectively fill therecess so that the outer surfaces of the mating region 114 andnon-mating region 115 are substantially flush, while in otherembodiments, more or less material is applied in the mating region. Whenthe material comprising the shaft and the material applied in the matingregion are similar, curing the assembly can lead to the integration ofthe two materials into a single, continuous mating region.

Additional material 130 can be the same material as in sheet 116 or canbe a different material. In one embodiment, both the sheet 116 andadditional material 130 are comprised of fiber-reinforced resin,although either one may separately be comprised of such material. Thefiber-reinforced resin of the sheet 116 and additional material 130 canbe anisotropic based on the orientations of the fibers, and may beapplied such that fibers in the additional material 130 arepreferentially oriented circumferentially so as to increase theresistance of the additional material to radial expansion. Additionalmaterial 130 may be applied so that fibers of the fiber-reinforced resinextend substantially completely around shaft 110, potentially providingmore resistance to radial expansion of mating region 114. Preferentialorientation in this case refers to the fact that a significant number offibers tend to be oriented generally circumferentially, although not allof the fibers necessarily need to be so oriented. Additional material,whether of the same or different composition as the previously-appliedmaterial, can be applied in the mating region either after the materialcomprising the mating and non-mating region of the shaft, as shown,before the material comprising the mating and non-mating region of theshaft, or can be interspersed or interleaved with layers of materialcomprising the mating and non-mating region of the shaft. Further,curing of the various layers of material can be completed all at once,in stages including any combination of the layers, or by performing acure step subsequent to the application of each additional layer.

A tubular sleeve 140 is provided, and the assembly of shaft 110 andfitting 120 are inserted through a lumen 142 defined by sleeve 140.Sleeve 140 can be applied from the shaft side, as shown, or from thefitting side of the member. In some cases, sleeve 140 is slightlytapered, as are the coupling region 122 and mating region 114. Eitherthe entire sleeve 140 can be tapered, or only the inner surface 141 ofsleeve 140 may be tapered and substantially parallel with the outersurface 118 of the shaft 110. This allows the sleeve 140 to slide ontoshaft 110 and come into increasingly close contact with the shaft and/orfitting, i.e., there is increasing interference between the shaft 110and the sleeve 140 as the sleeve 140 slides further onto shaft 110.Fitting may include a shoulder 126 (FIG. 2) for impeding the sleeve 140as it slides onto shaft 110. This provides a physical manner ofaccurately locating the position of the sleeve 140 relative to the shaft110. A section of reduced width 144 (FIG. 2) can be included in sleeve140 to assure proper contacting of sleeve 140 and shoulder 126. Theapplied sleeve 140 is substantially concentric with shaft 110 andradially adjacent to mating region 114. This further serves to preventradial expansion or deformation of shaft 110. Sleeve 140 may be formedof a range of materials, including metals and composites. In someembodiments, no sleeve is applied, and instead more material is appliedto the mating region of the shaft.

Other methods for attaching the sleeve are also possible. For example,sleeve 140 can be press fit around shaft 110, fitting 120, or both. Thiscan be done at one or several discrete locations, or can be acompressing of the entire sleeve 140. In other embodiments, adhesive isapplied to one or both of sleeve 140 and shaft 110. This can be done toenhance the bonding between sleeve 140 and the other components, or canbe done in place of press-fitting, in order to secure sleeve 140 inplace. The application of adhesive is facilitated by the use of atapered sleeve and coupling region of fitting, as described above, asthis geometry allows the parts to gradually engage as the shaft isinserted through the sleeve.

Referring to FIGS. 6 and 7, in another embodiment of the presentinvention, a composite structural member 200 includes a shaft 210 and afitting 220, the fitting defining a depression 224. Depression 224 doesnot extend completely around the circumference of fitting 220, that is,the depression 224 is not radially symmetric so as to form a neck. Usingthe processes described above, the shaft 210 can be formed aroundfitting 220 such that the shaft 210 assumes the profile of the fitting220 with a portion of the shaft protruding into and engaging thedepression. Because the depression 224 is not radially symmetric, themechanical interference its presence causes between shaft 210 andfitting 220 inhibits both relative translation of the shaft 210 andfitting 220 as well as relative rotation. Along the lines of theembodiment illustrated in FIGS. 6 and 7, it should be noted that therecessed portions in all of the examples could also be protrusions thatact to similarly induce mechanical interference with the fitting andassociated shaft. Although the embodiment depicted in FIGS. 6 and 7 havea single depression, the fitting can include two or more depressionsand/or protrusions spaced circumferentially thereabout.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. For example, referring to FIG. 8, in oneembodiment of the process for creating a composite structural member300, a core structure 360 is disposed within the fitting in the generalarea where the shaft will later be formed. The core structure acts as atemplate, along with the fitting, around which the shaft is formed. Inthis way, the core 360 permanently forms part of the composite member300, being disposed in the lumen 312 formed by the shaft 310. Corematerial, for example, can be a polymeric structural foam, such that itscrush strength is sufficient to support the shaft during processingand/or use, while the weight added by the presence of the core isminimal.

The present invention also contemplates embodiments in which the fittingis not an end fitting, but rather is more centrally located in theshaft. Also, when used in conjunction with the sleeve, reinforcingmember can be any structure that couples the outer surface of the shaftin the area of the neck with the inner surface of the sleeve, such thatthe reinforcing member creates a mechanical stop for radial expansion ofthe shaft. Other processes are also available for forming the shaft,such as resin transfer molding of dry fiber pre-forms. In someembodiments, some or all of the coupling region of the fitting isradially asymmetrical so as to physically discourage relative rotationof the fitting and shaft. For example, the coupling region could berectangular or elliptical in cross section.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A composite structural member comprising: a fitting including acoupling region, the coupling region defining at least one recessedportion bounded by one or more non-recessed portions; and a tubularshaft having a mating region of stiffness greater than another region ofsaid shaft and defining a lumen, said fitting being disposed in thelumen such that the mating region mates with the coupling region of saidfitting, wherein said shaft and fitting are mechanically restrained fromat least some relative movement due to interference of said shaft andsaid fitting.
 2. A composite structural member according to claim 1,wherein the recessed portion extends circumferentially around saidfitting to form a neck.
 3. A composite structural member according toclaim 1, further comprising adhesive disposed between the couplingregion of said fitting and the mating region of said shaft.
 4. Acomposite structural member according to claim 1, wherein said shaft hasincreased thickness in the mating region relative to another region ofsaid shaft.
 5. A composite structural member according to claim 1,further comprising a sleeve coupled to said shaft for discouragingexpansion of the mating region of said shaft.
 6. A composite structuralmember according to claim 5, wherein said shaft has increased thicknessin the mating region relative to another region of said shaft and saidsleeve has a tubular inner surface that proximately surrounds at leastpart of said shaft, including at least part of the mating region.
 7. Acomposite structural member according to claim 6, further comprisingadhesive disposed between said shaft and sleeve.
 8. A compositestructural member according to claim 7, wherein said shaft and fittingand the tubular inner surface of said sleeve are tapered.
 9. A compositestructural member according to claim 7, wherein said fitting includes ashoulder, said sleeve contacts the shoulder, and the inner surface ofsaid sleeve is substantially parallel with an outer surface of saidshaft.
 10. A composite structural member according to claim 1, furthercomprising a core disposed in at least part of the lumen of said shaft.11. A composite structural member according to claim 1, wherein saidshaft is comprised of fiber reinforced material and the mating regionincludes an increased percentage of fibers oriented substantiallycircumferentially relative to another region of said shaft.
 12. Acomposite structural member according to claim 1, wherein said shaft iscomprised of resin-based material and said fitting is comprised ofmetal.
 13. A composite structural member comprising: a fitting includinga coupling region, the coupling region defining at least one of aprotrusion or a recessed portion bounded by one or more non-recessedportions; and a tubular shaft having a mating region and defining alumen, said shaft being comprised of material including reinforcingfibers and being configured to have a greater percentage ofsubstantially circumferential fibers in the mating region than inanother region of said shaft, wherein said fitting is disposed in thelumen of said shaft such that the mating region of said shaft mates withthe coupling region of said fitting and said shaft and fitting aremechanically restrained from at least some relative movement due tointerference of said shaft and said fitting.
 14. A structural memberaccording to claim 13, wherein the coupling region is radiallyasymmetrical.
 15. A structural member according to claim 13, furthercomprising a sleeve coupled to said shaft for discouraging expansion ofthe mating region of said shaft.
 16. A method for producing a compositestructural member, the method comprising: providing a fitting having acoupling region with an outer surface, the outer surface defining atleast one recessed portion bounded by one or more non-recessed portions;forming a shaft around said fitting such that a mating region of saidshaft is radially adjacent to the coupling region and mating with therecessed portion of the outer surface; and adding material to the matingregion.
 17. A method according to claim 16, wherein adding material tothe mating region comprises orienting the material such that fibers inthe material are preferentially oriented substantially circumferentiallywith respect to an axis defined by the shaft and applying the materialthus oriented to the mating region of the shaft.
 18. A method accordingto claim 16, further comprising applying a tubular sleeve around saidshaft such that said sleeve is substantially concentric with said shaftand radially adjacent to at least part of the mating region.
 19. Amethod according to claim 18, wherein applying said tubular sleevearound said shaft comprises inserting said shaft and fitting through alumen defined by said sleeve until said sleeve contacts a shoulder ofsaid fitting.
 20. A method according to claim 19, wherein the couplingregion of said fitting and said sleeve are tapered and furthercomprising applying adhesive to at least one of said reinforcing memberand said sleeve.
 21. A method according to claim 16, wherein formingsaid shaft comprises forming said shaft by one of the group consistingof: resin transfer molding and laying up of one or more sheets of dryfibers.
 22. A method according to claim 16, further comprising insertinga core structure into a fitting, and wherein the forming the shaftincludes forming around fitting and core structure.
 23. A methodaccording to claim 22, further comprising removing the core structuresubsequent to forming shaft.